Sommerville-Software-Engineering-10ed

360 Chapter 12 ■ Safety engineering
Fault class
Data faults
Control faults
Input/output faults
Interface faults
Storage management faults
Static analysis check
Variables used before initialization
Variables declared but never used
Variables assigned twice but never used between assignments
Possible array bound violations
Undeclared variables
Unreachable code
Unconditional branches into loops
Variables output twice with no intervening assignment
Parameter type mismatches
Parameter number mismatches
Nonusage of the results of functions
Uncalled functions and procedures
Unassigned pointers
Pointer arithmetic
Memory leaks
Figure 12.9
Automated static
analysis checks
and highlights these to the programmer. Though relatively simple, analysis based
on common errors can be very cost-effective. Zheng and his collaborators (Zheng
et al. 2006) analyzed a large code base in C and C++. They discovered that 90%
of the errors in the programs resulted from 10 types of characteristic error.
2. User-defined error checking In this approach, the users of the static analyzer
define error patterns to be detected. These may relate to the application domain
or may be based on knowledge of the specific system that is being developed.
An example of an error pattern is “maintain ordering”; for example, method A
must always be called before method B. Over time, an organization can collect
information about common bugs that occur in their programs and extend the
static analysis tools with error patterns to highlight these errors.
3. Assertion checking This is the most general and most powerful approach to
static analysis. Developers include formal assertions (often written as stylized
comments) in their program that state relationships that must hold at that point
in a program. For example, the program might include an assertion stating that
the value of some variable must lie in the range x..y. The analyzer symbolically
executes the code and highlights statements where the assertion may not hold.
Static analysis is effective in finding errors in programs but, commonly, generates a
large number of false positives. These are code sections where there are no errors but
where the static analyzer’s rules have detected a potential for error. The number of false
positives can be reduced by adding more information to the program in the form of assertions,
but this requires additional work by the developer of the code. Work has to be done
in screening out these false positives before the code itself can be checked for errors.
Many organizations now routinely use static analysis in their software development
processes. Microsoft introduced static analysis in the development of device